A metal-air battery 1 is formed of: a cylindrical water-supply cylinder 2; cylindrical negative electrode metal (- electrode) 3; an air electrode (+ electrode) 4 containing a metal oxide, such as a titanium oxide, as a reaction catalyst and having a porous structure; a ceramic-titanium oxide catalyst layer 5 formed on the external periphery of the air electrode (+ electrode) and emitting weak electromagnetic waves; a spacer 6; a bottom plate 7; an electrolyte 9; and a protective member 10 having permeability. The air electrode (+ electrode ) 4 includes a metal oxide, such as a titanium oxide, mixed as a reaction catalyst and has an electrolysis catalyst 12 porous structure. When oxygen activated by the titanium oxide is used for an electrode reaction by forming the ceramic-titanium oxide catalyst layer 5 emitting weak electromagnetic waves on the external periphery of the air electrode (+ electrode), the metal-air battery 1 excellent in power generation characteristics can be obtained.